Leftover food, including one’s own, is often painful to touch, let alone put into one’s mouth. Even children are grossed out, as the expression goes, by their own food left on the table. The prohibition is partly cultural, but it must have deep evolutionary roots. Food spoils quickly and leftover food can carry germs from one individual to another. Scavenging is for professionals, as it were. How painful it must be for a hungry and homeless person, like the one in front of me on Westbourne Grove, to reach into a garbage bin for the first time!